forces, which are the same as the chemical forces. The first is the combination between the forces themselves; the result of it is the contraction of the two forces, or their reduction to a smaller volume, with the disengagement of light and heat. The second is the combination of a product with a supporter. The result of it likewise is condensation, and the evolution of light and heat, though not to so great an extent as in the first case. The third degree consists in the combination of an alkali with an acid. It is rarely accompanied by the disengagement of light, but always with the disengagement of heat. A condensation likewise takes place unless peculiar causes modify the result. Expansion, which is the effect of a repulsive force in bodies, is most frequently owing to an excess of one of the electric forces. Contraction is the effect of an equilibrium between the forces, and of their mutual extinction.

The forces which produce the electrical and chemical actions of bodies are the same as those which produce the mechanical properties of bodies. Impenetrability depends on the resistance which the expansive power of two forces opposes to a body endeavouring to penetrate the space already occupied by another body. Cohesion is the effect of the two forces, which attract one another. Uni-. versal attraction consists in the action at a distance of the two forces upon each other, supposing the expansive power of each force not to extend beyond the surface of bodies.

Such is an abstract of M. Oersted's hypothesis, as far as I have been able to make it out. It is fair, however, to state, that I have not had an opportunity of perusing his own work, but only the abstracts of it published in some of the German journals, and an outline given by Van Mons in his translation of Sir H. Davy's Ele: mentary Work. Hence it is very possible that I may not have done the author justice, and that some of the parts of his hypothesis, which appear

the most whimsical and absurd, would assume another aspect under the explanations of the author himself. On that account I shall not attempt any critical examination of this hypothesis, which has given the author considerable celebrity in Ger. many. Its weak parts and inconsistencies are sufficiently obvious to those who have followed the late improvements in electricity and chemistry. The metaphysical part I do not fully understand; nor have I been able to make out whether the author's electrical forces be substances or qualities.

At present, then, it seems to be the prevailing opinion of chemists that chemical affinity is identical with electrical attraction. The opinion possesses much plausibility, and even probability; but much remains to be done before it can be considered as established, and made the foundation of our chemical reasonings.

II. Proportions in which Bodies combine chemically.-That the ultimate particles of matter consist of atoms, incapable of farther subdivision, is an opinion which has been pretty generally received among philosophers ever since the time of the Greeks; and since the establishixent of the Newtonian philosophy, this opinion has

al forces. The first is the es; the result of it is the · reduction to a smaller

and heat. The second is -porter. The result of it ation of light and beat, be first case. The third alkali with an acid. It is

of light, but always with etion likewise takes place

Expansion, which is the ost frequently owing to an traction is the effect of their mutual extinction. 1 and chemical actions of e the mechanical proper on the resistance which s to a body endeavouring apother body. Cohesion

become almost universal. That substanees always enter into chemical combination, in determinate proportions which never vary, has been known ever since chemists acquired the art of analysing bodies. Thus carbonate of lime, wherever, or in whatever state, it occurs, is always a compound of 43.2 carbonic acid and 57.8 lime; and sulphate of barytes, of 34.5 sulphuric acid and 65.5 barytes. In like manner, the yellow oxide of lead is always a compound of 100 lead and 7-7 oxygen; and red oxide of mercury, of 100 mercury and 8 oxygen. Sulphuric acid is always composed of three parts of oxygen and two parts of sulphur ; and carbonic acid, of

; 2000 oxygen and 751 carbon. This law is universally admitted by chemists, and, indeed, the more rigorously it has been examined, the more conspicuous and decided have become the proofs in its favour. Even Berthollet, who seems to be an enemy to the atomic theory in the abstract, has admitted that all known compounds unite in determinate proportions; and has endeavoured to reconcile this fact to his own opinions by several highly ingenious, and some rather whimsical, arguments. The few exceptions which he was able to muster up against the law have all disappeared before the more rigid and exact examination of modern analysts.

Mr. Dalton was the first person who ventured to account for this fixedness in chemical proportions. According to him, it is the atoms of bodies that unite together. One atom of a body, a, unites with one atom of a body, l, or with two atoms of it, or with three, four, &c. atoms of it. The union of one atom of a with one atom of U produces one compound, the union of one atom of a with two atoms of l produces another compound, and so on. Each of these compounds, of course, must consist of the same proportions, because the weight of every atom of the same body must of necessity

act one another. Unit a distance of the two nsive power of each force

a

be the same.

We have no means of demonstrating the number of atoms which unite together in this manner in every compound; we must, therefore, have recourse to conjecture. If two bodies unite only in one proportion, it is reasonable to conclude that they unite atom to atom. Hence it is most likely that water is composed of one atom of

oxygen and one atom of hydrogen ; oxide of silver, of one atum silver and one atom oxygen; and oxide of zinc, of one atom zinc and one atom oxygen.

When a body has the property of uniting with varivus doses of oxygen, we can then determine the number of atoms which constitute the compounds. Thus manganese unites with four doses of oxygen; and supposing the manganese to be represented by 100, the oxygen of each respective oxide is represented by the numbers 14, 28, 42, 56; but these numbers are to each other as the numbers one, two, three, four. Hence the first oxide is composed of one àtom manganese and one atom oxygen; the second, of one atom manganese and two atoms oxygen; the third, of one atom manganese and three atoms oxygen; and the fourth, of one atom manganese and four atoms oxygen. In like manner, as mercury

ing opinion of chemists rical attraction. The probability; but much ed as established, and ngs. chemicalsy.-- That the

incapable of farther etty generally received e Greeks; and since pby. this opinion has

2

one.

combines with two doses of oxygen, and forms two oxides, the first composed of 100 mercury and four oxygen, and the second of 100 mercury and eight oxygen, it is obvious that the first must be a compound of one atom mercury and one atom oxygen, and the second of one atom mercury and two atoms oxygen.

Nor is there any difficulty with respect to iron. There are two oxides of that metal : the first composed of 100 iron and 28 oxygen; the second of 100 iron and 42 oxygen. Now as 28 is to 42 as two to three, it follows that the first is a compound of one atom iron and two atoms oxygen; the second, of one atom iron and three atoms oxygen. The same rule holds good with respect to the oxides of nickel and cobalt.

If we know the number of atoms of which a body is combined, and the proportion of the constituents, there is no difficulty in determining the proportional weight of the atoms of which it is composed. Thus if water be composed of one atom of oxygen and one

' atom of hydrogen, and if the weight of the oxygen in water is to that of the hydrogen as 7; to one, then it follows that the weight of an atom of exygen is to that of an atom of hydrogen as 71 to

If black oxide of mercury, be composed of one atom of mercury and one atom of oxygen, and if it be composed of 100 mercury and four oxygen, then an atom of mercury is to the weight of an atom of oxygen as 100 to four, or as 25 to one. If black oxide of iron be composed of one atom iron and tivo atoms oxygen, and if it consist of 100 iron and 28 oxygen, then an atom of iron is to an atom of oxygen as 100 to 14, or as 7.142 to one. Such is the method of determining the weight of an atom of the different substances upon which experiment has hitherto been made. The advantage of such a knowledge is immense; because it gives us the proportions in which the different substances unite together, and even enables us to calculate the proportional constituents of all compound bodies, independent of experiment, and with more accuracy than would result from experiments unless conducted with uncommon precautions.

Hitherto the only persons who have written upon the subject of chemical atoms are Mr. Dalton, Sir Humphry Davy, Dr. Berzelius, Dr. Wollaston, and myself. Mr. Dalton made choice of hydrogen as his unit, hecause it is the lightest of all the atoms; and Sir H. Davy has followed his example. But as oxygen enters into a much greater number of compounds than any other body,

it was chosen by Dr. Wollaston and Dr. Berzelius as the most convepient unit; and in the tables of atoms which I have published in the different volumes of the Annals of Philosophy, I have followed their example. Berzelius considers an atom of oxygen to weigh 100, Wollaston makes it weigh 10, and I myself make its weight one. The reader will perceive that these three numbers are the same, the only difference being the position of the decimal point. : The

person who has hitherto made the greatest number of experiments upon this important subject is Dr. Berzelius; and he has

1

is comand one ter ist = weight 28 7; to

atom of

of 100 weight f black atoms

considered himself as entitled, by the results which he has obtained, to establish two propositions which he considers as axioms or chemical first principles, and which have a prodigious influence on the whole doctrine. These axioms are the following :-

1. In all compounds of inorganic matter one of the constituents is always in the state of a single atom. According to this axiom, no inorganic compound is ever composed of two atoms of a united with three atoms of l, or of three atoms of a united with four atoms of 19,&c.; but always of one atom of a united with one, two, three, four, &c. atoms of b. This axiom, if it hold good, which Berzelius thinks it will, greatly simplifies the doctrine of atomic combination, as far as inorganic bodies are concerned, and reduces the whole to a state of elementary facility.

2. When an acid unites to a base, the oxygen in the acid is always a multiple of the oxygen in the base by a whole number, and generally by the number denoting the atoms of oxygen in the acid. Thus sulphuric acid contains three atoms of oxygen : 100 parts of it contain 60 oxygen ; and 100 parts of sulphuric acid combine with, and saturate, a quantity of base which contains 20 oxygen. Now 20 multiplied by three, the number of atoms of oxygen in sulphuric acid, makes 60 the quantity of oxygen in 100 of sulphuric acid.

Such are the two axioms of Berzelius, which he has made the foundation of his whole reasoning, and from which he has deduced his rules for determining the proportion of oxygen in bodies, and the number of atoms of which they are composed. If they bold good, and hitherto they have answered wonderfully well, they must be admitted to be of the utmost importance, and to give a facility and elegance to our chemical investigations which could scarcely have been looked for.

Mr. Dalton, the founder of the atomic theory, has not adopted either of these axioms. At the same time he has not advanced any fact in opposition to them; but only that there is nothing in the atomic theory which necessarily leads to their adoption. This is doubtless true. The axioms are merely empyrical, and deductions from analyses. Yet if they hold in all the analyses hitherto made, we cannot well refuse them a good deal of generality; and the best mode of proceeding seems to be to admit them till some exception to them be discovered.

Berzelius, considering the atomic theory to labour under difficultięs, which in the present state of our knowledge we are not able to surmount, bas substituted in its place another, which he conceives to be easier and simpler. This may be called the theory of volumes. He conceives bodies to be all in the gaseous state, and embraces the opinion of Gay-Lussac, that gaseous bodies always unite in volumes that are aliquot parts of each other. One volume of one body always unites with one, two, three, &c. volumes of another. How this alteration, which consists merely in the substitution of the word volume for atom, simplifies the atomic theory, or

ject of Berzeice of toms; enters

removes any of the difficulties under which it labours, is, I own,
beyond my comprehension. But Berzelius has deserved so well of
chemistry, that he may be indulged in any innocent whim which
produces no deterioration.
I should take
up too much room were I here to give a table of the

a
weights of the atoms of bodies. I must satisfy myself with referring
to the different papers which I have inserted in the Annals of Phi-
losophy on the subject, to the paper of Berzelius in the third
volume of the Annals, in which will be found his table of the
weights of an atom of the simple substances, and to Dr. Wollas-
ton's scale of chemical equivalents. The weights given in these
three different tables do not always coincide with each other; but
in general a very near approach to coincidence will be perceived.
In some cases the weights that I have assigned are half those
given by Berzelius. The reason of this is obvious; and the cir-
cumstance can occasion no difficulty or ambiguity.

II. Light and Heat. In the account of the progress of chemistry which I gave at the beginning of last year, I had to state a considerable number of important additions to the doctrine of heat, and its connection with light; but at present this department of the science is nearly barren. M. Berard has repeated and confirmed the experiments of Dr. Herschel on the heating power of the different rays of solar light. He found the greatest heating power at the extremity of the red ray. He likewise repeated the experiments of Wollaston, Ritter, and Böckman, on the deoxidizing power of the solar rays. He found it greatest, as they had done, in the violet ray; and traced it in a diminishing rate to the middle of the spectrum, where it disappeared.

Morichini, a Roman chemist, announced some time ago that, when steel needles are exposed

to the action of the violet ray, they are converted into magnets

. This experiment has been repeated in France, but has not been attended with success. HII. Simple Supporters and Combustibles with their Compounds.

There are a considerable number of facts to relate respecting this branch of chemistry.

1. Iodine.--This singular substance was discovered some years ago by M. Courtois, a saltpetre manufacturer in Paris. It was first examined by Clement and Desormes, then by Sir H. Davy, and lastly by Gay-Lussac. It is obtained from kelp by a very easy process, which has been described in the Annals of Philosophy, French kelp yields it in much greater abundance than British kelp. Hence it would appear that the sea plants that yield it are more abundant in the English Channel than on the east or west coast of Britain. Iodine is in small crystals, which Dr. Wollaston has ascertained to be octahedrons. It has the metallic lustre, and resembles plumbago in colour, though its lustre is considerably